Cellular systems in the Long Term Evolution (LTE) and LTE-Advanced specifications not only provide for cellular communications as between a mobile terminal and a base station, but also, for communications between mobile terminals. Referred to as device-to-device or “D2D” communications, mobile terminals may communicate with one another utilizing a direct radio link in addition to the cellular communication. While the cellular communications utilize frequency division duplexing (FDD) mode, these D2D communications utilize time division duplexing (TDD) duplex mode with the base station controlling the use of the uplink (UL) and downlink (DL) resources of the cellular network. The end result of providing for such D2D communications is reduced transmitter power consumption for both the base station and the mobile terminals, increased cellular network capacity and improved services for the users, and thus, D2D communications are expected to become very popular as the demands on our wireless communications networks increase faster than the capacity of these networks.
Packet scheduling mechanisms for wireless networks providing such a “hybrid” environment may be quite challenging for a number of reasons. Traditional cellular systems with only cellular devices in the network typically utilize a “proportional fair” or “PF” packet scheduler. The PF metric to assign mobile terminals in a PF packet scheduler is based on the ratio of the instant signal to interference plus noise ratio (SINR) based criteria and throughput based criteria. Thus, the PF metric can be expressed as the following equation, wherein j is the jth transmission time interval (TTI)/the current TTI:PFmetric(j)=InstSINR(j)/AvgSINR
While providing a fair comparison for all cellular devices, using techniques such as the PF scheduler to divide and scheduling resources in such a hybrid network poses several difficulties. Because of dynamic channel conditions in D2D connections and also, associated levels of interference, mobile terminals in a D2D connection will have a higher PF metric. In this regard, the PF metric distribution for mobile terminals with a D2D connection may be much wider because of more dynamic changes in the channel conditions and the interference, mainly from the cellular users. As a mobile terminal with a D2D connection may experience severe interference from the neighboring cellular and D2D transmissions at some TTIs, the average SINR decreases greatly. Consequently, during the other TTIs in which the mobile terminals with a D2D connection experiences less interference, the PF metric will generally be fairly high in comparison with cellular users. Thus, utilizing the PF metric in hybrid network will usually result in choosing the D2D users over cellular users, and thus, packets from D2D mobile terminals may be overscheduled.